1. Technical Field
This invention generally relates to systems for processing blood and other biological fluids.
2. Background Art
Centrifugal biological-fluid-processing systems have been in existence for some time. Some are used to collect high concentrations of certain components of a person""s blood while others are used to further process blood components by washing, concentrating or otherwise purifying the blood component of interest. Some of these systems are used to process biological fluids other than blood. Filtration systems are also used for processing blood and other biological fluids.
The centrifugal systems (hereinafter called blood-processing systems) generally fall into two categories, continuous-flow devices and discontinuous-flow devices.
In continuous-flow systems, whole blood from the donor or patient flows through one conduit into the spinning rotor where the components are separated. The component of interest is collected and the unwanted components are returned to the donor through a second conduit on a continuous basis as more whole blood is being drawn. Because the rate of drawing and the rate of return are substantially the same, the extracorporeal volume, or the amount of blood that is out of the donor or patient at any given time in the procedure, is relatively small. These systems typically employ a belt-type rotor, which has a relatively large diameter but a relatively small (typically 100 ml or less) processing volume. Although continuous-flow systems have the advantage that the amount of blood that must be outside the donor or patient can be relatively small, they have the disadvantage that the diameter of the rotor is large. These systems are, as a consequence, large; furthermore, they are complicated to set up and use. These devices are used almost exclusively for the collection of platelets.
In discontinuous-flow systems, whole blood from the donor or patient also flows through a conduit into the rotor where component separation takes place. These systems employ a bowl-type rotor with a relatively large (typically 200 ml or more) volume that must be filled with blood before any of the desired components can be harvested. When the bowl is full, the drawing of fresh blood is stopped, and the unwanted components are returned to the donor or patient through the same conduit intermittently, in batches, rather than on a continuous basis. When the return has been completed, whole blood is again drawn from the donor or patient, and a second cycle begins. This process continues until the desired amount of component has been collected.
Discontinuous-flow systems have the advantage that the rotors are relatively small in diameter but have the disadvantage that the extracorporeal volume is large. This, in turn, makes it difficult or impossible to use discontinuous systems on people whose size and weight will not permit the drawing of the amount of blood required to fill the rotor. Discontinuous-flow devices are used for the collection of platelets and/or plasma, and for the concentration and washing of red blood cells (RBCs). They are used to reconstitute previously frozen RBCs and to salvage RBCs lost intraoperatively. Because the bowls in these systems are rigid and have a fixed volume, however, it is difficult to control the hematocrit of the final product, particularly if the amount of blood salvaged is insufficient to fill the bowl with RBCs.
One RBC-washing system marketed by Cobe Laboratories is made almost entirely of flexible PVC. It has the advantage of being able to vary the volume of the rotor to control the final hematocrit but has the disadvantage of being limited to a rather flat, wide pancake-like shape due to manufacturing constrictions. The Cobe system controls the rotor volume by pumping a hydraulic fluidxe2x80x94a liquidxe2x80x94in or out of a bladder that rotates with and squeezes the blood out of rotor. The Cobe system takes up a fairly large amount of space, and its flexible pancake-shaped rotor is awkward to handle. The Cobe system does not permit blood to flow into and out of its rotor at the same time. The Cobe system also does not permit blood to be pulled into the rotor by suction. The Cobe rotor is usually filled with blood by gravity, although the blood may be pumped into the rotor. After the blood has been separated, it is squeezed out of the rotor by pumping hydraulic fluid into the bladder.
Haemonetics Corp. and others have provided systems to collect blood shed during surgery, concentrate and wash the RBCs, and return them to the patient. Existing systems typically use a 3 liter reservoir to collect and coarse filter the blood vacuumed from the surgical site and a separate processing set including a special centrifugal processing chamber to wash and concentrate the red blood cells in order that they may be safely reinfused to the patient. Because of their cost and complexity of use, these systems are used only in operations where relatively large blood loss is expected. The prior-art rotors used for processing blood collected during an operation, made by Haemonetics Corp. and others, must be completely filled with RBCs before any processing can occur, and thus the process takes more time and is not appropriate for use with small people or for an operation with low blood loss. Because the volume of the processing chamber is fixed, the final concentration of the RBCs in the last cycle of the process cannot be easily controlled.
Solco Basel AG makes a filter-based system for wound drains. This wound-drain system has the disadvantage that the blood returned to the patient contains, in addition to the RBCs, substances that may be deleterious to the patient.
There exists the need, therefore, for a centrifugal system for processing blood and other biological fluids, that is compact and easy to use and that does not have the disadvantages of prior-art discontinuous-flow systems. There is also a need for improving the way that blood is processed in a variety of applications, such as apheresis, intraoperative blood-salvage systems, and wound drains, so that the blood processing takes less time, requires less cumbersome equipment, and/or reduces harmful side effects in the patient or donor.
The present invention provides a container, referred to herein as a rotor, which may be used for collecting and centrifuging biological fluids in a range of volumes. The rotor includes an elastic impermeable wall (diaphragm) which defines at least a portion of a variable-volume processing chamber, where the fluid is centrifuged. The rotor includes a rigid mounting member, to which the diaphragm is mounted and which is held and spun by a chuck. Preferably, this rigid mounting member includes a wall which together with the elastic diaphragm defines the chamber.
This diaphragm and rigid wall are both referred to herein as boundaries, since each defines a portion of the boundary of the variable-volume processing chamber and each has one side which does not come into contact with the biological fluid. In some embodiments, the diaphragm may be located inside other walls on the exterior of the rotor, such as the rigid boundary wall or an exterior shell.
The rigid boundary wall may be large enough to surround the maximum volume that may be taken up by the chamber, or the rigid mounting member may be only large enough to provide a place where the diaphragm may be mounted and where a chuck can hold and spin the rotor. In a preferred embodiment, the rigid boundary wall is a substantially imperforate circular wall which extends to the periphery of the processing chamber, so as to define the top of the processing chamber; the diaphragm is attached to the perimeter of the wall and defines the remainder of the processing chamber.
As noted above, the rigid wall in one embodiment surrounds the chamber, and the diaphragm is located inside a portion of the rigid boundary wall. In one version of this embodiment, the rotor includes a core located inside the rigid boundary wall and the chamber, and the diaphragm is mounted about the core.
In a preferred embodiment, the rigid boundary wall is substantially imperforate but defines one opening, preferably near the axis of rotation, permitting a conduit or conduits to pass therethrough so as to be in fluid communication with the processing chamber. In another alternative embodiment, the rigid boundary wall has a plurality of openings for controlling the flow into and/or out of the rotor while the rotor is being spun.
Preferably, the rotor includes a separate structure for controlling the flow of liquid out of the chamber into the rotor""s (outlet) conduit. In a preferred embodiment, this outlet-control structure is a perforate, substantially rigid wall or plate, located within the processing chamber and mounted adjacent the rigid boundary wall. Since it is located within the processing chamber, and both of its sides come into contact with the biological fluid, this perforate wall is referred to as an interior wall. The perforate interior wall preferably extends substantially to the periphery of the chamber, although in other embodiments it may have a smaller diameter. Although in a preferred embodiment the perforate wall has many holes, in alternative embodiments the perforate wall may have holes located only at a discrete radius or at discrete radii from the axis of rotation. The interior wall may also serve the purpose of protecting the elastic membrane from being abraded from a non-rotating portion of the rotor while the body of the rotor is spun.
In an alternative embodiment, the outlet-control structure for controlling flow from the processing chamber to the conduit includes at least one tube or preferably a set of tubes, wherein each tube provides fluid communication between the chamber and the conduit. The tubes used as the outlet-control structure may have holes along their length to provide additional points of entry for fluid from the processing chamber. In some versions of the rotor, the tube or tubes provide fluid communication from a variety of radii within the chamber; in other versions, the tube or tubes provide fluid communication from a discrete radius or discrete radii within the chamber.
In another preferred embodiment, the outlet-control means may include vertical walls that define channels. These channels may be grooves formed in the interior surface of the rigid boundary wall. As long as the vertical channel walls are spaced close enough to each other (i.e., as long as the grooves are narrow enough), the channels (grooves) will remain open even though the processing chamber is at its lowest volume and the elastic membrane is pressed against the bottom of the vertical walls. Such channels can provide fluid communication to the rotor""s outlet conduit from the periphery of the processing chamber to the innermost radius of the processing chamber and all the points in between. The grooves can be shortened so as to provide fluid communication to the outlet conduit from just those points between two radii within the chamber.
In one embodiment of the rotor, a single conduit passes through a portion of the rotor that does not rotate during centrifugationxe2x80x94i.e., the rotor""s fixed portion. The fixed portion passes through the rigid boundary wall, and the rigid boundary wall is rotatably mounted around the fixed portion. In another embodiment, two or more conduits pass through a portion of the rotor that does not rotate during centrifugation. This embodiment permits unseparated fluid to flow into the spinning rotor through one conduit, while separated fluid can flow out of the rotor through the other conduit. This embodiment of the rotor may further include a substantially imperforate interior wall, mounted between the boundary wall and the perforate interior wall and around the fixed portion, so as to provide a channel permitting fluid to flow from the rotor""s input conduit to the chamber""s periphery. This substantially imperforate interior wall does define a center hole through which the rotor""s fixed portion passes. The substantially imperforate interior wall may be considered an inlet-control structure which controls the flow of fluid into the rotorxe2x80x94in this case directing the fluid to the rotor""s periphery.
Alternative embodiments of the rotor do not have a fixed portion. The conduits extending from these embodiments of the rotor thus spin with the rest of the rotor during centrifugation. A rotary seal may be located at some point in the tubing connecting the rotor with the rest of the processing set. Alternatively, a skip-rope system may be used in lieu of a rotary seal.
The embodiments of the rotor having a fixed portion preferably include a rotary seal that has a base, a spring member, first and second seal faces, which spin in relation to each other, and a flexible seal member. The spring is mounted on the base, and the first seal face is mounted on the spring member so that the spring member presses the first seal face against the second seal face. The seal member prevents flow between the first seal face and the base. Preferably, the flexible seal member and the first seal face are disposed so that the force with which the spring member presses the first seal face against the second seal face is not adversely affected by pressure within the rotor. In a preferred embodiment, the flexible seal member and the spring member are separate members, although they may be made out of different portions of the same piece of material. Alternatively, if the flexible seal member is resilient and rigid enough to apply the proper force between the first and second seal faces, a separate spring member may not be necessary.
In one embodiment, the rotary seal""s base is part of the rotor""s fixed portion, and the rotary seal""s second seal face is attached to the rigid mounting member, which is part of the rotating portion of the rotor. Alternatively, the rotary seal""s base may be part of the rotor""s rigid mounting member, and the rotary seal""s second seal face is attached to the rotor""s fixed portion.
The rotor may be spun in a centrifuge system that includes a chuck for holding and spinning the rotor and a pressurized fluid supply for supplying a pressurized control fluidxe2x80x94preferably gasxe2x80x94adjacent the rotor""s diaphragm, while the rotor is being spun. The pressurized gas may be used to force fluid out of the rotor""s processing chamber. The system preferably includes means for applying a vacuum to the exterior side of the diaphragm (i.e., the side that does not come into contact with the fluid being processed), so as to draw fluid into the processing chamber. In one embodiment, for use with a rotor where the diaphragm is mounted along the bottom of a substantially flat, circular boundary wall, the chuck has extending from a rotatable base an outer peripheral wall, so as to define a cylindrical cavity into which the diaphragm may expand. In one version of this chuck embodiment, the chuck also has extending from its base a core, so that the chuck defines an annular cavity into which the diaphragm may expand. In another embodiment, for use with a rotor that has a core in the rotor""s interior, the chuck has extending from a rotatable base a nozzle, through which the pressurized gas is provided through the rotor""s core to an area adjacent the rotor""s diaphragm. Another embodiment of the chuck holds the rotor from inside a rigid core in the rotor.
In order to make the rotor more portable while biological fluid is being collected in the rotor, a rigid, airtight exterior shell may be attached and sealed to the rigid boundary wall. In one embodiment, the shell may be removably attached to the rotor. The shell permits a vacuum to be applied to the exterior side of the diaphragm when the rotor is not in a chuck. Thus, fluid may be drawn into the processing chamber when the rotor is not in a chuck. A spring bellows may also be used to create a vacuum against the diaphragm.
The system may also include a control system for controlling the rotational speed of the chuck and the gas pressure provided by the gas supply to achieve the most advantageous combination of centrifugal force for separation and gas pressure against the diaphragm required to force fluid out of the rotor. The control system may be programmed to determine the volume of the processing chamber based on the rotational speed of the chuck and the air pressure provided by the chuck.
The rotor and centrifuge systems of the present invention may be used in many different processes involving biological fluid. A method for using the rotor would generally include the steps of introducing an unseparated fluid into the rotor""s processing chamber, spinning the rotor so as to separate the fluid into denser and lighter components, and applying pressure to the diaphragm""s exterior side so as to force a fluid componentxe2x80x94usually the lighter fluid componentsxe2x80x94through the conduit.
Further aspects of the present invention will be apparent from the following description of specific embodiments, the attached drawings and the appended claims.